Traditional at-home cleaning techniques for dental hardware include brushing by hand or placing the hardware in a solution with tablets that acidify and effervesce. Such tablets may be comprised of, for example, an inorganic bleach, sodium perborate, with a coloring agent, preservatives, flavor, and a catalyst or two. When sodium perborate is placed in water, it reacts to form a mild solution of hydrogen peroxide, while releasing oxygen. These techniques for cleaning hardware can also reduce the potential for odor to the extent that they destroy bacteria.
The methodology of employing ultra-high frequency sound waves or mechanical movement as a means to impart low-amplitude motion to objects or fluids for dislodging particulate matter has been known for many years. The basic equipment for this technique includes a power generating unit and one or more piezoelectric crystals-elements or electromechanical motors. Vibration of the piezoelectric crystal-element is accomplished when direct current (DC) is applied across the piezoelectric crystal. Once electrically polarized, the crystal deforms axially in the direction of the polarization. If the electrical current is halted and then reverse biased, the crystal returns first back to its null position and proceeds to deform to the same magnitude in the opposite direction along a single linear axis. If the current is repeatedly applied and then reversed, the crystal, and hence the piezoelectric element, will oscillate back and forth along a single axis at the frequency of the reversing applied current.
The normal range of human hearing is between 20 and 20,000 cycles per second (CPS, Hertz, or Hz). Vibratory motion of solids or fluids below 20 Hz is below the threshold of human hearing and is defined as being subsonic. Vibratory motion within the 20 Hz to 20,000 Hz band is within the range of human hearing and is, by definition, sonic. Vibratory motion above the 20,000 Hz threshold is considered to be in the ultrasonic range, or that which is beyond the ability of human hearing. Thus, for example the application of reversing current at a frequency of 20,000 Hz or greater to a piezoelectric crystal-element will generate linear oscillatory motion in the low ultrasonic region. If the piezoelectric crystal-element is surrounded by relatively inviscid fluid in a container, the oscillatory motion will be transferred to the fluid, and standing waves of a peak-to-peak period, in seconds, of ½π times the applied current frequency will result. The amplitude of the standing waves is increased by increasing the applied voltage to the crystal-element. Thus, cyclic motion of the inviscid fluid may be generated to the degree desired by establishing the frequency of electrical stimulation and the voltage applied to the piezoelectric crystal-element.
Being in motion relative to any large body submerged within it, the fluid imparts molecular agitation to the body's exterior surface or surfaces, along with all particulate matter that is mechanically attached to it. With repeated exposure to the agitated fluid, these particulates will become dislodged over time. In such a manner, a cleaning effect of the body occurs, to the extent that, in general terms, particles that are beyond the physical reach of mechanical brushes or removal tools can be dislodged by the motion of the fluid bath.
Similar ultrasonic motion may be generated by electromechanical means by using a small single-pole or multi-pole, direct-current or alternating-current motor, onto whose rotor one or more eccentric weights have been affixed, or, alternately, onto whose rotor eccentric weight has been removed. The rotor is thus in a dynamically unbalanced state when rotated, due to the inertial force of the weight, or absence of it, as the rotor is rotated in a circular path. This inertial imbalance, formed over a two-dimensional plane perpendicular to the rotor's axis, is transferred through the motor's bearings and into its stator and mounting frame. Thus, for example, with the application of the correct DC voltage to the unbalanced motor to achieve a rotational speed in excess of 20,000 RPM, vibratory motion of the motor itself in the low ultrasonic frequency range (20,000 Hz) can be achieved. The amplitude of the vibratory motion is governed by the quantity and radial position of the weight imbalance in the rotor and the DC voltage applied to the motor windings. If surrounded by a relatively inviscid fluid in a container, as was the case with the piezoelectric crystal-element previously described, oscillatory motion of that fluid will result. However, due to the fact that the inertial force of the motor's rotor imbalance is directed in a plane rather than a single line, the amount of physical motion imparted to the fluid typically is comparatively greater than that produced by a piezoelectric crystal. Motion can be imparted in a manner such that the vector of fluid momentum continually changes direction, repeating a 360-degree cycle with each revolution of the rotor. Thus, a body submerged in a vibrating fluid bath will experience a cleaning effect, due to the repetitive impact of fluid molecules onto the body's surface.
Patents describing systems that employ high-frequency movement and relative motion, piezoelectric crystals-elements or unbalanced DC motors, and aqueous solutions and baths for imparting ultrasonic cleaning include Smith, U.S. Pat. No. 5,534,741 and Puskas, U.S. Pat. No. 6,181,052. U.S. Pat. No. 5,534,741 describes in some detail a timed piezoelectric ultrasonic device and residence tank for cleaning jewelry. A piezoelectric element is pulsed so as to effect cleaning of the jewelry by varying and increasing the agitation of a solution bath in which it is submerged. The device described in U.S. Pat. No. 6,181,052 is similar to that of U.S. Pat. No. 5,534,741 in that an ultrasonic transducer (in the case of U.S. Pat. No. 6,181,052, three transducers) creates ultrasonic motion of a fluid bath into which an object is placed, thus effecting cleaning of that object. The device is intended for use with unidentified “delicate parts.” The frequency of oscillations is intentionally varied to cause physical dislodging of particulates attached to an object immersed within the bath tank.
Winston, U.S. Pat. No. 5,853,290 is representative of techniques in which a tool is ultrasonically vibrated to dislodge particles from an object, such as a tooth, that cannot be physically removed and placed within a liquid bath. An ultrasonic element is used to agitate fluid enclosed within a hermetically sealed flexible tube, onto the end of which the tool itself is affixed. The ultrasonic vibration of the liquid, and hence the tool, is accomplished by a remotely mounted power generating unit to which the liquid-filled tube is affixed. Thus, once energized, the tool may be positioned in any orientation or position, while axial ultrasonic vibration of the tool head continues unabated.
In the above-described systems, cleaning of the body in question is performed via the agitation of a liquid bath surrounding that body, this agitation being lineally transferred from an axially vibrating element to the liquid itself.
In accordance with advances in technology, liquid baths and the object or objects being cleaned may be subjected to direct ultraviolet (UV) radiation, so as to effect irradiative sterilization action. One or more direct-acting antibacterial chemicals in the bath may also be used, to effect chemical sterilization action concurrently with the irradiative action. Ultrasonic cleaning by piezoelectric or like means may also be incorporated.
Fuesting, U.S. Pat. No. 4,448,750 improves upon the generalized ultrasonic cleaning technique by the addition of an ultraviolet bulb in the device that irradiates a liquid bath from above with light at a preferred wavelength of 2537 angstroms (253.7 nanometers), for the purpose of concurrently cleaning and sterilizing medical and dental instruments. This patent also prescribes the content of the cleaning-sterilizing fluid, and in particular those constituents in water that would offer the best transmittance of the UV radiation from the bulb through the fluid and onto the item or items being cleaned and sterilized. Hydrogen peroxide (H2O2) is specifically excluded as a preferred constituent or additive to the bath because, according to the patent, the transmittance of H2O2 to UV radiation is less than 1 percent, while the desired transmittance of the liquid solution to ultraviolet radiation should be greater than twenty percent. Thus, the intent is to effect sterilization of an item by direct contact of the item with the solution bath, concurrently with direct UV irradiation of the item, and not as an indirect consequence of UV absorption by the cleaning solution itself. The dental instruments shown in the Fuesting patent appear to be of the type commonly used in dentist's offices, which frequently cause bleeding of gums. Thus, sterilization is of particular importance to avoid infection to the patient through the patient's blood system.
The apparatus of the Fuesting patent, which is a modified version of a relatively large and bulky and commercially available ultrasonic bath, is intended for use in a dentist's office or similar environment. Because of its size and relatively non-portable construction, the apparatus does not lend itself to at-home use by consumers. Because the fluid-filled cleaning chamber occupies the entirety of the base of the apparatus, the entire apparatus must vibrate during use and, furthermore, the cleaning chamber cannot be removed from the rest of the apparatus or serve as a portable storage container. Rather, it appears that the medical or dental practitioner must retrieve the individual medical or dental instruments, or a tray carrying multiple instruments, from the inside of the base of the apparatus. Although the Fuesting patent mentions that the top cover of the apparatus can be lined with reflective material, it seems that a certain percentage of the ultraviolet radiation would be dispersed in the form of heat.
H2O2 irradiated by UV light results in the near-complete absorption of the UV light, leading to molecular photolysis of H2O2 into constituent hydroxyl (OH) radicals. The chemical interaction of these free, and extremely aggressive, hydroxyl radicals with bacteria and viruses causes the destruction of these pathogens by altering, among other things, their DNA structures. Once chemically altered by the OH radicals, these pathogens either die immediately or quickly mutate such that they cannot replicate, in effect dying shortly afterwards. Thus, although H2O2 is an effective biocide by itself, and UV irradiation is effective in killing bacteria and viruses by itself, the combination of H2O2 irradiated by UV light can produce a far greater biocidal effect due to photolysis and the creation of sterilizing hydroxyl free radicals. The biocidal effect also has been found to be useful for the remediation and cleanup of water containing hazardous levels of dissolved organic materials.
Baron, U.S. Pat. No. 5,120,499 describes a small, compact system for asepticizing contact lenses, in which the contact lenses are placed in a weak solution of hydrogen peroxide (no greater than 30 parts per million) and exposed to ultraviolet radiation from an ultraviolet source behind which a reflector is mounted. Ultrasonic vibration of the lenses is employed to cause dislodgement of microorganisms from the lenses, but the patent does not state that the ultrasonic vibration is used as the cleaning method for the lenses (such that traditional cleaning or rinsing would not be required). The background section of the Baron patent indicates that prior asepticization techniques, such as chemical treatment, were focused primarily on preventing damage to the contact lenses themselves rather than preventing infection of the eyes or of other parts of the human body by exposure of the eyes to micro-organisms (direct contact of eyes with micro-organisms being a very common cause of infection). The contact lens receptacle tray is not suitable for receiving dental hardware.